Australia Post says 40 tonnes of mail are currently waiting to be airlifted to destinations affected by the volcanic ash cloud.
National Manager External Affairs Alex Twomey says Australia Post has been unable to airlift any mail to Europe since April 16.
However, the airlines are aiming to airlift international mail as soon as possible, Mr Twomey told SBS.
"The estimated delay for mail deliveries is unknown and is entirely dependent on flight capacities, fuel and passenger requirements now that airlines are resuming their services".
"Our Sea Mail service is only applicable for the delivery of parcels and is offered as a cheaper solution when speed of delivery is not important. Given the length of time it would take to ship the delayed items by sea, it is preferable that we airlift these items as soon as capacity is available," Mr Twomey said.
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Australia Post says it cannot estimate the costs of flight disruptions due to volcanic ash.
DHL says normal service standards apply for any shipments picked up from today.
DHL Express Oceania's Senior Vice President, Gary Edstein, told SBS customers with shipments already in progress have been told to expect a 24-72 hour delay for shipments moving intra Europe and a three-five day delay for shipments moving into and out of Europe from/to the rest of the world.
In areas still affected by the closure of airspace, DHL says it will continue to serve customers through an alternative and decentralised road-based network.
